1. Field of the Invention
The present invention relates to a cutting oil composition for processing a cemented carbide skiving hob. More particularly, this invention relates to a cutting oil composition for cemented carbide skiving hob which contains at least one specific additive and has a specific viscosity.
2. Description of the Prior Art
Cemented carbide skiving hob cutting is a relatively new processing technique as a finishing process for gears. Conventional techniques in the processing of gears having a relatively high module for use in construction machinery or shipbuilding have required the five steps of (1) rough processing, (2) finishing processing, (3) quenching, (4) shaving, and (5) honing. According to the novel technique of the present invention, the processing of gears can be accomplished using the four steps of (1) rough processing, (2) quenching, (3) skiving, and (4) honing. Furthermore, since the novel technique provides gears of high precision within a shorter period of time than that required using conventional techniques, it has been rapidly employed for the past several years in many countries.
A skiving hob results from the attachment of tips to an ordinary hob so as to adjust the rake angle of the hob to -30.degree.. Therefore, cutting is made at an angle of -30.degree., and the surface of a gear of high hardness can also be finished well. Moreover, it is considered that wear of the cutting edge is slight. The details of this processing manner are described in articles appearing in Gears (the 8th Symposium of the Japan Society of Mechanical Engineers, Sendai, Japan, Aug., 1975, Article No. 750-9, pp 115-122) and Japanese Patent Publication No. 15800/75.
It is common knowledge that in cutting processing using cemented carbide tools, cutting oils are not used because the cemented carbide tools have poor resistance to heating-cooling thermal shock, and cooling readily causes cracks or breakage of the cutting edge. Thus, no cutting oil is used at all in cemented carbide skiving hob processing.
On the other hand, where this cemented carbide skiving hob processing (for brevity, such processing is hereinafter merely referred to as "SK processing") is performed without using cutting oils, disadvantages occur in that the precision of the finished gear profile becomes poor due to an elevation of the temperature of the workpieces, etc., and the life of the tool is extremely short. For this reason, use of suitable oils for the purpose of increasing the processing precision has been heretofore been desired.
According to present research, it was found that when ordinary gear cutting oils are used in SK processing, compression collapse (a kind of chipping) occurs partly on the cutting edge of the tool to thereby shorten the life of the tool, and, as a result, processing precision decreases.
As a result of extensive investigations to develop cutting oils suitable for such a kind of processing, it was found that by employing a base oil having a lower viscosity than that of known gear cutting oils and blending a certain additive thereto, the life of cutting tools can be prolonged and the precision of gears can be increased, and the present invention can be accomplished.